/*
wav编码器+编码引擎
https://github.com/xiangyuecn/Recorder

当然最佳推荐使用mp3、wav格式，代码也是优先照顾这两种格式
浏览器支持情况
https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats

编码原理：给pcm数据加上一个44直接的wav头即成wav文件；pcm数据就是Recorder中的buffers原始数据（重新采样），16位时为LE小端模式（Little Endian），实质上是未经过任何编码处理
*/
(function () {
	'use strict';

	Recorder.prototype.enc_wav = {
		stable: true,
		testmsg: '支持位数8位、16位（填在比特率里面），采样率取值无限制'
	};
	Recorder.prototype.wav = function (res, True, False) {
		var This = this,
			set = This.set,
			size = res.length,
			sampleRate = set.sampleRate,
			bitRate = set.bitRate == 8 ? 8 : 16;

		//编码数据 https://github.com/mattdiamond/Recorderjs https://www.cnblogs.com/blqw/p/3782420.html https://www.cnblogs.com/xiaoqi/p/6993912.html
		var dataLength = size * (bitRate / 8);
		var buffer = new ArrayBuffer(44 + dataLength);
		var data = new DataView(buffer);

		var offset = 0;
		var writeString = function (str) {
			for (var i = 0; i < str.length; i++, offset++) {
				data.setUint8(offset, str.charCodeAt(i));
			}
		};
		var write16 = function (v) {
			data.setUint16(offset, v, true);
			offset += 2;
		};
		var write32 = function (v) {
			data.setUint32(offset, v, true);
			offset += 4;
		};

		/* RIFF identifier */
		writeString('RIFF');
		/* RIFF chunk length */
		write32(36 + dataLength);
		/* RIFF type */
		writeString('WAVE');
		/* format chunk identifier */
		writeString('fmt ');
		/* format chunk length */
		write32(16);
		/* sample format (raw) */
		write16(1);
		/* channel count */
		write16(1);
		/* sample rate */
		write32(sampleRate);
		/* byte rate (sample rate * block align) */
		write32(sampleRate * (bitRate / 8)); // *1 声道
		/* block align (channel count * bytes per sample) */
		write16(bitRate / 8); // *1 声道
		/* bits per sample */
		write16(bitRate);
		/* data chunk identifier */
		writeString('data');
		/* data chunk length */
		write32(dataLength);
		// 写入采样数据
		if (bitRate == 8) {
			for (var i = 0; i < size; i++, offset++) {
				//16转8据说是雷霄骅的 https://blog.csdn.net/sevennight1989/article/details/85376149 细节比blqw的按比例的算法清晰点，虽然都有明显杂音
				var val = (res[i] >> 8) + 128;
				data.setInt8(offset, val, true);
			}
		} else {
			for (var i = 0; i < size; i++, offset += 2) {
				data.setInt16(offset, res[i], true);
			}
		}

		True(new Blob([data.buffer], { type: 'audio/wav' }));
	};
})();
